Many patients benefit from receiving therapeutic gas (e.g., nitric oxide gas) in inspiratory breathing gas flow from a breathing circuit affiliated with a ventilator (e.g., constant flow ventilator, variable flow ventilator, high frequency ventilator, bi-level positive airway pressure ventilator or BiPAP ventilator, etc.). To provide therapeutic gas to a patient who receives breathing gas from a ventilator, the therapeutic gas may be injected into the inspiratory breathing gas flowing in the breathing circuit. This inhaled therapeutic gas is often provided via a therapeutic gas delivery system as a constant concentration, which is provided based on proportional delivery of the therapeutic gas to the breathing gas. Further, a sampling system (e.g., affiliated the therapeutic gas delivery system) may continuously draw in the inspiratory breathing gas flow to at least confirm that the desired dose of the therapeutic gas in the inspiratory breathing gas flow is being delivered to the patient. For example, a sample pump may pull in inspiratory flow (e.g., in the near vicinity of the patient) to confirm that the desired therapeutic gas concentration is in fact being delivered to the patient in need thereof.
One such therapeutic gas is inhaled nitric oxide (iNO). In many instances iNO is used as a therapeutic gas to produce vasodilatory effect on patients. When inhaled, nitric oxide (NO) acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. Because of this, nitric oxide is provided in inspiratory breathing gases for patients with various pulmonary pathologies including hypoxic respiratory failure (HRF) and persistent pulmonary hypertension (PPH). The actual administration of iNO is generally carried out by its introduction into the patient as a gas along with other normal inhalation gases, for example, by introducing iNO, from an iNO delivery system, into the inspiratory flow of a patient breathing circuit affiliated with a ventilator.
Separately and/or in conjunction with iNO, patients may receive inspiratory breathing gas flow containing liquid particles (e.g., nebulized medical solutions and suspensions, moisture from humidified air, etc.) and/or other particles. Although this matter in the inspiratory breathing flow may provide additional benefit to the patient, they may contaminate the sampling system (e.g., gas analyzers) of the therapeutic gas delivery system used to confirm dosing of iNO being delivered to the patient. Unlike the mere filtering of liquids from gas, filtering these contaminates from the sampled inspiratory breathing gas flow can be substantially difficult. Filtration design complexities or difficulties may include the desire for very low internal and external leakage, very low resistance to flow, and materials compatibility such that filter materials used do not adulterate the gas sample to be analyzed. Low internal and external leakages are critical in this application, as nitric oxide (NO) is monitored in the range of 1 to 80 parts per million (ppm) and nitrogen dioxide (NO2) in the range of 1 to 5 ppm. A small external leak, for example, may dilute the sample to be analyzed, potentially rendering inaccurate sample gas analysis. A small internal leak may allow contaminant to pass through the filter, resulting in potential performance degradation of downstream pneumatic controls and/or gas analyzer sensors, also having the potential of rendering inaccurate sample gas analysis. Low filter resistance to flow is critical as this attribute relates directly to pump power requirements. Lower resistance to flow enables smaller pumps consuming less power to be used, resulting in smaller, lighter, quieter medical devices. The impact of lower power components can be compounded for devices requiring battery back-up, allowing for use of smaller batteries. Medical device pumps operating at lower sound pressure levels can be especially advantageous in settings such as the ICU, where quiet operation is critical to the clinical staff. Other competing physical attributes from User's perspective are desire for longevity (e.g., infrequent filter changes would come with larger filters) in contrast with desire for compact device (which may require smaller filters). Adding complexity, the sampled inspiratory flow is typically required throughout treatment (e.g., constant or near constantly sampling of the inspiratory flow just prior to, in the immediate vicinity of, entry into the patient) to provide real time, or near real time, confirmation of dosing during therapeutic gas delivery to the patient.
Accordingly, at times, there is a need to filter the sampled inspiratory breathing gas flow of liquid particles and/or other particles, for example, to mitigate contamination of the gas sampling system. Further, there may also be other uses for an improved apparatus and method that can effectively filter at least these, or other, contaminants from sampled inspiratory breathing gas flow being provided to a patient in need thereof.